1. Field of the Invention
The present invention relates to High Performance Liquid Chromatography (HPLC) and the other analytical methods involving flowing liquid streams which are well known techniques for separating the constituent elements in a given sample. More specifically, the present invention relates to prime/purge, injection, and column selections valves used in HPLC systems.
2. Background Information
FIG. 1, a block diagram illustrates a typical environment in which the present invention will be utilized, with the elements of a prior art HPLC system shown. Liquid solvent 31 (often called the "mobile phase") is introduced from a solvent reservoir 32 and delivered via tubing 33 to a pump 34. This pump creates a vacuum which draws the solvent through the tubing and into the pump. The solvent will then exit the pump at a much higher pressure (typically in the range between 500 and 7000 psi) and then passes the solvent through a prime/purge valve 35.
As the name suggests, a prime/purge valve when opened permits priming of the pump during system startup by simply venting the pump outlet to atmospheric pressure via a waste outlet 36. An alternate method of priming the pump is by connecting a large syringe or other vacuum generating device to this waste outlet 36 and drawing the solvent from the reservoir through the pump 34. The other function of a prime purge valve is to permit rapid solvent change-out by allowing the purging of the pump and associated plumbing of any unwanted solvent.
After the prime/purge valve, a sample injection valve 37 permits loading a sample into a sample loop 38, using a syringe 39 or other metering device. When the valve is switched to the inject position, the sample contained within the sample loop is transferred at high pressure into a chromatographic column 41 or 42.
In some HPLC systems a column switching valve 40 is incorporated to permit the selection between two or more columns 41 and 42 and to permit various flow routes through these columns.
When the sample that was introduced via the injection valve is carried through a column (along with the mobile phase), the various components (solutes) in the sample migrate through the column at different rates due to the solute's affinity to the column packaging material. Because of the different rates of movement of the solutes, the sample components gradually separate as they move through a column. After exiting the column, the sample (as separated) is carried to a detector 43 which detects the presence or absence of various ions or molecules.
In these analytical methods, it is desired to minimize the holdup volume of the system and to eliminate any unswept volumes in the flow path. The minimized holdup volume is desired because it facilitates the rapid and complete replacement of one solvent for another and efficient gradient mixing. Unswept volumes are avoided, as an unswept volume can allow diffusion of sample into the unswept area or allow diffusion of carrier fluid (or a previous sample) out, thus diluting the sample and decreasing the resolution and sensitivity of the analytical method.
FIG. 5A, is prior art which illustrates one type of sample injection valve with an associated prime/purge valve. The injection valve includes a disc shaped rotor with three circumferential channels on its front face. The rotor face extends perpendicular to its axis of rotation, which lies face wise adjacent to the face of a stator. The stator has six ports which lie on a port circle and extend axially to a rear face. An external sample loop of known volume can be connected to two of these ports. A sample can then be introduced to the sample loop through one of the stator ports thus filling the sample loop. When the rotor is turned 60.degree. (FIG. 5B), solvent from a high pressure pump pumps the sample through the sample loop and corresponding stator passages into the chromatographic column. Model 7010 of Rheodyne L. P. (see Rheodyne Catalog #6 Page 6) is an example of such an injector. FIG. 5C illustrates the associated prime/purge valve in the open position. Flow from the pump, bypasses the injector valve and column entirely, and is directed to a waste container where the back pressure is essentially atmospheric. This prior art injector permits sample injection into a chromatographic system but requires an additional prime/purge valve to permit the priming or purging of a pump.
Fogelman describes a valve (U.S. Pat. No. 5,105,851) which could permit both sample injection and prime/purge capabilities but Fogelman's design does not permit flushing of the sample port when the valve is in the inject position. FIG. 13A and 13B show a Fogelman design in both the "LOAD" and "INJECT" positions respectively. FIG. 13B shows that when the valve is in the inject position, any sample remaining in port 51 can not be flushed since the port is dead ended against the rotor seal. This inability to flush the sample port 51 would be undesirable since any sample remaining in the port from a previous injection would cause contamination of the next sample to be loaded. There is a need for a single multi-position valve that permits both sample injection and prime/purge capabilities thus reducing the overall system holdup volume.
FIGS. 9A and 9B are prior art for one type of column selection valve which includes a disc shaped rotor with three circumferential channels on its front face that lies face wise against the stator rear face. Pivoting the rotor 60.degree. enables these channels to connect to different columns depending on the position of the valve. FIG. 9A shows the column selection valve with flow passing through column A while column B is connected head to tail. When the rotor is pivoted 60.degree. as shown in FIG. 9B, column A is now connected head to tail, and flow passes through column B. Model 7000 of Rheodyne L. P. (see Rheodyne Catalog #6 Page 17) is an example of this type of column selection valve. This valve has no unswept volume in any part of the flow path, but selection is limited to only two alternate paths.
In some chromatographic analysis where large sample volumes are injected, it may be desirable to use a sample concentration scheme known as sample enrichment. FIGS. 8A and 8B are prior art for this concentration scheme which consists of injecting large volumes of sample into a pre-column, where trace components are concentrated. FIG. 8A shows an injector valve which can inject a large sample onto the head of the pre-column where the sample can be concentrated. Simultaneously, flow from a second pump delivers solvent through an analytical column. After valve switching (FIG. 8B), the enriched sample is back flushed off the pre-column and onto the analytical column by use of the second pump.
Fogelman's valve when plumbed as a column selector permits the selection between 2 or more columns and a bypass. The disadvantage of this design is that since there is always a single peripheral stator port that is dead-ended to the rotor seal in every position, this prevents the "off-line" columns from being connected head-to-tail, thus allowing the pressure in these columns to decay. Those knowledgeable in the field of chromatography would agree that in many instances, it is desirable to maintain pressure in the "off-line" column to facilitate the rapid re-equilibration of the column when it is brought back "on-line".
There exists a need for a multi-route selection valve that permits sample enrichment using a single pump and permits selection between two columns and a bypass.